<?php

class Session
{

    protected $sess_expiration; // session id time to live (TTL) in seconds
    protected $sess_time_to_update; // session time to update in seconds
    protected $flashdata_key = 'flash'; // prefix for "flash" variables (eg. flash:new:message)
    protected $CI;

    public function __construct($params = array())
    {

        $this->CI = & get_instance();

        if (!$this->sess_expiration = (isset($params['sess_expiration'])) ? $params['sess_expiration'] : $this->CI->config->item('sess_expiration'))
        {
            $this->sess_expiration = 7200;
        }
        
        if (!$this->sess_time_to_update = (isset($params['sess_time_to_update'])) ? $params['sess_time_to_update'] : $this->CI->config->item('sess_time_to_update'))
        {
            $this->sess_time_to_update = 300;
        }

        log_message('debug', "MY_Session Class Initialized");
        $this->_sess_run();
    }

    /**
     * Regenerates session id
     */
    public function regenerate_id()
    {
        // copy old session data, including its id
        $old_session_id = session_id();
        $old_session_data = $_SESSION;

        // regenerate session id and store it
        session_regenerate_id();
        $new_session_id = session_id();

        // switch to the old session and destroy its storage
        session_id($old_session_id);
        session_destroy();

        // switch back to the new session id and send the cookie
        session_id($new_session_id);
        session_start();

        // restore the old session data into the new session
        $_SESSION = $old_session_data;
        
        // update the session creation time
        $_SESSION['regenerated'] = time();

        // session_write_close() patch based on this thread
        // http://www.codeigniter.com/forums/viewthread/1624/
        // there is a question mark ?? as to side affects
        // end the current session and store session data.
        session_write_close();
    }

    /**
     * Destroys the session and erases session storage
     */
    public function destroy()
    {
        unset($_SESSION);
        if (isset($_COOKIE[session_name()]))
        {
            setcookie(session_name(), '', time() - 42000, '/');
        }
        session_destroy();
    }
    
    /**
     * Alias of destroy()
     */
    public function sess_destroy()
    {
        $this->destroy();
    }
    
    /**
     * Return all session
     */
    public function all_userdata()
    {
        return $_SESSION;
    }

    /**
     * Reads given session attribute value
     */
    public function userdata($item)
    {
        if ($item == 'session_id')
        { //added for backward-compatibility
            return session_id();
        }
        else
        {
            return (!isset($_SESSION[$item])) ? false : $_SESSION[$item];
        }
    }

    /**
     * Sets session attributes to the given values
     */
    public function set_userdata($newdata = array(), $newval = '')
    {
        if (is_string($newdata))
        {
            $newdata = array($newdata => $newval);
        }

        if (count($newdata) > 0)
        {
            foreach ($newdata as $key => $val)
            {
                $_SESSION[$key] = $val;
            }
        }
    }

    /**
     * Erases given session attributes
     */
    public function unset_userdata($newdata = array())
    {
        if (is_string($newdata))
        {
            $newdata = array($newdata => '');
        }

        if (count($newdata) > 0)
        {
            foreach ($newdata as $key => $val)
            {
                unset($_SESSION[$key]);
            }
        }
    }

    /**
     * Starts up the session system for current request
     */
    protected function _sess_run()
    {
        session_start();

        // check if session id needs to be expired
        if ($this->_session_id_expired())
        {                        
            // destroy session
            return $this->destroy();                        
        }        
        
        // check if session id needs regeneration
        if ($this->_session_id_need_updated())
        {            
            // regenerate session id (session data stays the
            // same, but old session storage is destroyed)
            $this->regenerate_id();
        }
        
        // delete old flashdata (from last request)
        $this->_flashdata_sweep();

        // mark all new flashdata as old (data will be deleted before next request)
        $this->_flashdata_mark();
    }

    /**
     * Checks if session has expired
     */
    protected function _session_id_expired()
    {
        if (!isset($_SESSION['regenerated']))
        {            
            $_SESSION['regenerated'] = time();
            
            return false;
        }

        return ($_SESSION['regenerated'] + $this->sess_expiration) <= time();                
    }
    
    /**
     * Checks if session need to be updated
     */
    protected function _session_id_need_updated()
    {
        if (!isset($_SESSION['regenerated']))
        {
            $_SESSION['regenerated'] = time();
            return false;
        }
        
        return ($_SESSION['regenerated'] + $this->sess_time_to_update) <= time(); 
    }
    
    /**
     * Sets "flash" data which will be available only in next request (then it will
     * be deleted from session). You can use it to implement "Save succeeded" messages
     * after redirect.
     */
    public function set_flashdata($key, $value)
    {
        $flashdata_key = $this->flashdata_key . ':new:' . $key;
        $this->set_userdata($flashdata_key, $value);
    }

    /**
     * Keeps existing "flash" data available to next request.
     */
    public function keep_flashdata($key)
    {
        $old_flashdata_key = $this->flashdata_key . ':old:' . $key;
        $value = $this->userdata($old_flashdata_key);

        $new_flashdata_key = $this->flashdata_key . ':new:' . $key;
        $this->set_userdata($new_flashdata_key, $value);
    }

    /**
     * Returns "flash" data for the given key.
     */
    public function flashdata($key)
    {
        $flashdata_key = $this->flashdata_key . ':old:' . $key;
        return $this->userdata($flashdata_key);
    }

    /**
     * PRIVATE: Internal method - marks "flash" session attributes as 'old'
     */
    protected function _flashdata_mark()
    {
        foreach ($_SESSION as $name => $value)
        {
            $parts = explode(':new:', $name);
            if (is_array($parts) && count($parts) == 2)
            {
                $new_name = $this->flashdata_key . ':old:' . $parts[1];
                $this->set_userdata($new_name, $value);
                $this->unset_userdata($name);
            }
        }
    }

    /**
     * PRIVATE: Internal method - removes "flash" session marked as 'old'
     */
    protected function _flashdata_sweep()
    {
        foreach ($_SESSION as $name => $value)
        {
            $parts = explode(':old:', $name);
            if (is_array($parts) && count($parts) == 2 && $parts[0] == $this->flashdata_key)
            {
                $this->unset_userdata($name);
            }
        }
    }

}